The background art will be described by taking a slewing drive device of a shovel as an example.
A shovel comprises a crawler-type lower traveling body, an upper slewing body mounted on the lower traveling body in such a manner as to be slewable about an axis perpendicular to a ground surface, and a work attachment attached to the upper slewing body.
A slewing drive device of the shovel is designed to cause slewing of the upper slewing body. The slewing drive device comprises: a hydraulic or electric motor as a drive source; and a speed reducer equipped with a gear mechanism operable to reduce a speed of rotation of the motor, and configured to transmit the rotation reduced in speed by the gear mechanism to the upper slewing body as a driven unit.
The motor and the speed reducer are arranged side-by-side in an axial direction of the slewing drive device in such a manner that respective rotational axes thereof are aligned with each other. The motor and the speed reducer are attached to an upper frame in a vertical posture where the motor is disposed above the speed reducer.
The speed reducer comprises a single-stage or multi-stage planetary gear-type speed reducing unit having a sun gear, a planetary gear and a ring gear. An output of the speed reducer is transmitted to the upper slewing body, thereby causing slewing of the upper slewing body.
The speed reducer has a casing containing lubricating oil therein. Based on this lubricating oil, lubrication of the single or multi-stage speed reducing unit (planetary gear mechanism) is performed. During operation of the slewing drive device, according to a centrifugal force and a pumping action caused by a movement of the speed reducing unit, a part of lubricating oil in the casing, specifically, a portion of the lubricating oil located on the side of an outer periphery thereof, is urged to rise along an inner wall surface of the casing, so that an oil surface of the lubricating oil in the casing has an inverted cone shape, or the lubricating oil in the casing is splattered upwardly. This phenomenon becomes more violent as a temperature of lubricating oil increases, and therefore an oil level thereof rises.
In the lubricating oil in the casing, the upraised portion located on the side of the outer periphery, a portion, immediately falls inwardly under its own weight, and returns to the speed reducing unit. This lubricating oil returning to the speed reducing unit causes an increase in resistance against the speed reducing unit when it agitates lubricating oil during an operation thereof. This results in giving rise to a problem of an increase in energy loss occurring during the operation of the speed reducing unit.
As a technical means to solve this problem, there have heretofore been known a technique disclosed in the follow Patent Literatures 1 and 2.
In this heretofore-known technique disclosed in these Patent Literatures, a tank is provided outside a casing, and an upper passage and a lower passage with a restricted orifice are provided to extend between an inside and an outside of the casing. Based on this configuration, a portion of lubricating oil upraised to cause an oil surface of the lubricating oil to have an inverted cone shape is introduced into the tank via the upper passage and stored in the tank, and then the lubricating oil stored in the tank is returned to the inside of the casing via the lower passage.
However, in above heretofore-known technique, in the portion of the lubricating oil upraised over the entire inner periphery of the casing to cause the oil surface of the lubricating oil to have an inverted cone shape, only a limited part of the upraised lubricating oil is introduced into the tank via the narrow upper passage, so that the upraised lubricating oil does not reach the tank unless the entire lubricating oil is agitated by a certain level or more of agitating force. Therefore, an amount of oil to be stored becomes small. This results in deterioration of an effect of reducing energy loss occurring when the speed reducing unit agitates lubricating oil.
Moreover, in the above heretofore-known technique, the tank, the upper passage and the lower passage are provided outside the casing, so that a slewing drive device will be complicated in structure and increased in size, as a whole. This is likely to cause a significant increase in production cost of the slewing drive device, and exert negative influences on peripheral layout of the slewing drive device.
Further, in the above heretofore-known technique, from the standpoint of suppressing an increase in size of the slewing drive device, it is not allowed to increase the size of the tank. In this respect, an amount of lubricating oil storable in the tank becomes smaller, and therefore the energy loss reducing effect becomes more deteriorated.